High-sensitivity measuring instrument and method of using the instrument to measure a characteristic value at a point in time

ABSTRACT

A high-sensitivity measuring instrument comprising at least two sensors for detecting the same characteristics by touching a substance being measured with a specified time difference, wherein the between detection signals taken out simultaneously from respective sensors is determined, the difference between characteristic values upon elapsing the specified time difference is determined from the difference between detection signals, a reference time of measurement and a reference characteristic value at that time are preset, a time axis having a time pitch of a specified time difference is set, and a measurement value is obtained at a point in time elapsing an arbitrary time pitch from the reference time. Objective measurement characteristics can be detected by the measuring instrument not in the form of difference or variation but as an absolute value with high accuracy and sensitivity.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a high-sensitivity measuring instrumentwhich detects a variation in characteristic of a substance beingmeasured such as an aqueous solution with high sensitivity and accuracy,and can detect the characteristic value itself at that time with highsensitivity and accuracy based on the detected value of the variation incharacteristic.

BACKGROUND ART OF THE INVENTION

As characteristics of a substance being measured, for example, anelectric conductivity is used as, in particular, a scale for measuring aconcentration of an ion capable of moving in an aqueous solution, and anelectric conductivity measuring instrument is used for measurement ofion concentration of many aqueous solutions. Generally, the electricconductivity measuring instrument determines increase/decrease of ionconcentration of an aqueous solution being measured by measuring aresistance between a detection electrode and an electrode for supplyinga current from a power source.

In a case where a variation of electric conductivity or a difference inelectric conductivity between a plurality of positions being measured isdetermined by using a conventional electric conductivity measuringinstrument, when the variation or the difference is small as comparedwith an absolute value of the electric conductivity being measured,because the measurement range of the instrument is being adjusted for arelatively large absolute value of electric conductivity, themeasurement of a fine variation or difference is very difficult, or themeasurement data are very poor in reliability. In practice, however,there are much demands for determining such a fine difference orvariation between two or more measurement points different from eachother in position or in time, and if such a fine difference or variationcan be measured with a high reliability and with high accuracy andsensitivity, such measurement would find wide application.

Accordingly, in order to satisfy the above-described demands, theapplicant of the present invention previously proposed a multi-dimensionelectric conductivity measuring instrument in JP-A-2001-311710 as aninstrument capable of abstracting and determining a variation ofcharacteristics of a substance being measured such as an aqueoussolution with a high accuracy. This multi-dimension electricconductivity measuring instrument comprises at least two electricconductivity measuring cells each having at least two electrodes cominginto contact with a substance being measured, and the electricconductivity measuring cells are electrically connected to each other sothat the detection signals themselves from the respective electricconductivity measuring cells are processed by at least addition orsubtraction.

In this instrument, to the detection signals themselves from therespective electric conductivity measuring cells, namely, to thedetection signals themselves abstracted simultaneously, the electricalprocessing such as addition or subtraction is carried out, and thesignals after the processing, being amplified as needed, are outputtedas a difference or a variation between measured electric conductivitiesof the respective electric conductivity measuring cells. Because adifference between detection signals abstracted simultaneously isoutputted, it becomes possible to detect a variation with a high S/Nratio by erasing a noise commonly generated in the respective electricconductivity measuring cells, and it becomes possible to output only thedifference or the variation at a high accuracy, by amplification, etc.Therefore, in this instrument, unlike an arrangement wherein a pluralityof conventional electric conductivity measuring instruments are disposedand a difference or variation between the data measured therefrom isobtained, a fine difference or variation between electric conductivitiesof a plurality of measurement points different in position or in timefrom each other can be determined with a high reliability and with highaccuracy and sensitivity.

Although the invention disclosed in the above-described JP-A-2001-311710was proposed for measurement of electric conductivity, the technology bywhich a difference or variation in characteristics to be measured isdetermined with a high reliability and with high accuracy andsensitivity by outputting a difference between detection signalssimultaneously taken out from at least two sensors, can be appliedbasically to measurement of any characteristic.

However, the indicated value in the multi-dimension electricconductivity measuring instrument proposed by the above-describedJP-A-2001-311710 is a fine difference or variation between electricconductivities in a plurality of measurement points different inposition or in time from each other, and such an indicated value is notan absolute value of electric conductivity. In practice, however, avariation in absolute value of electric conductivity is frequentlyrequired for measurement of variation in concentration of impurities inan aqueous solution, etc. Even when a characteristic other than theelectric conductivity is determined, measurement of absolute value ofthe characteristic is frequently required.

DISCLOSURE OF THE INVENTION

Accordingly, paying attention to the fact that a fine difference orvariation in characteristics of a substance being measured can bedetermined with a high accuracy by the technology proposed by theabove-described JP-A-2001-311710, and assuming that such a technology ispractical, an object of the present invention is to provide a measuringinstrument which can further determine not a difference or variation buta measurement value of an objective characteristic with high accuracyand sensitivity, desirably, as an absolute value.

To accomplish the above object, a high-sensitivity measuring instrumentaccording to the present invention comprises at least two sensors fordetecting the same characteristics by bringing them into contact with asubstance being measured with a specified time difference, wherein adifference between detection signals abstracted simultaneously fromrespective sensors is determined, a difference between characteristicvalues upon elapsing the specified time difference is determined fromsaid difference between detection signals, a reference time ofmeasurement and a reference characteristic value at that time arepreset, a time axis having a time pitch of the specified time differenceis set, and a measurement value is obtained at a point in time elapsingan arbitrary time pitch from the reference time.

In the above-described high-sensitivity measuring instrument, it ispossible to obtain only a measurement value at a certain time as a valuedetermined by adding an amount of variation from the reference time tothe reference characteristic value at the reference time, and it is alsopossible to obtain measurement values as data in time sequence atrespective points in time elapsing respective time pitches from thereference time.

Further, in a case of obtaining the measurement values as data in timesequence, the data in time sequence may comprise a plurality of groupsof data in time sequence including data in time sequence, a position ofa time pitch of which is present within the above-mentioned specifiedtime difference. In such an embodiment, it is possible that theplurality of groups of data in time sequence can output measurementvalues at respective points in time elapsing respective time pitches inthe direction of the time axis with a pitch smaller than theabove-mentioned specified time difference, and it becomes possible toindicate the variation of the measurement value as if it were acontinuous variation.

Further, in the above-described high-sensitivity measuring instrument,it is necessary to set a reference characteristic value at a referencetime, and various methods for setting this reference characteristicvalue can be employed. For example, a substance being measured forreference is brought into contact with the sensors, and an output valuethereof in the measuring instrument can be set as the referencecharacteristic value. In this case, even if the characteristic value ofthis substance being measured for reference is not known, by using asubstance being measured for reference adequate for comparing it with anobjective substance being measured, it becomes possible to determinewhat value the characteristic value of the objective substance beingmeasured becomes relative to the characteristic value which thesubstance being measured for reference has, thereby obtaining at least arelative value compared with the substance being measured for reference.

Alternatively, it is also possible to bring a substance being measuredfor reference having a known characteristic value (for example, ultrapure water, etc.) into contact with the sensors, and to set thereference characteristic value so that an output value thereof becomesthe known characteristic value in the measuring instrument according tothe present invention. By thus contacting a substance being measured forreference having a known characteristic value, it becomes possible tocalibrate the reference characteristic value with a high accuracy.

Therefore, by using a substance being measured for reference whosecharacteristic value is not known or a substance being measured forreference whose characteristic value is known as described above, forexample, even in a case where there is a fear that an initially setreference characteristic value may drift with a lapse of a long periodof time, it becomes possible to correct the drift at an appropriateinterval in time, and whereby it becomes possible to carry outmeasurement or monitoring always at a high accuracy.

In the present invention, the substance being measured is notparticularly restricted, but the present invention can be easily appliedparticularly to a case where it is a fluid.

In such a high-sensitivity measuring instrument according to the presentinvention, since firstly a difference between detection signalssimultaneously abstracted from at least two sensors touching a substancebeing measured with a specified time difference is outputted, only avariation of an objective characteristic value at a certain time, forexample, at the present time, is detected at high sensitivity andaccuracy. The technical concept up to this step is substantially thesame as that proposed in the aforementioned JP-A-2001-311710. In thepresent invention, further, a difference between characteristic valuesupon elapsing the specified time difference is determined from theabove-described difference between the detection signals, a referencetime of measurement and a reference characteristic value at that timeare preset, the above-mentioned specified time difference is set as atime pitch, and a measurement value is obtained at a point in timeelapsing an arbitrary time pitch from the reference time (namely, at apoint in time elapsing an arbitrary time pitch at which an output as themeasurement value is required). This measurement value is obtained as avalue calculated by setting the reference characteristic value as areference of the measurement, and as long as an absolute value is set asthe reference characteristic value, the measurement value is obtainedalso as an absolute value of characteristic value. In other words, theabove-described variation in time of the characteristic detected at highsensitivity and accuracy at the specified time difference is added tothe reference characteristic value at the reference time, and thefinally outputted signal indicates a variation of the absolute value ofthe characteristic detected precisely at this variation in time, and itbecomes possible to detect the target absolute value itself at a highsensitivity and a high accuracy.

Namely, in the high-sensitivity measuring instrument according to thepresent invention, it becomes possible to determine a variation ofcharacteristic of a substance being measured at a high sensitivity and ahigh accuracy, in particular, as an absolute value. Therefore, anabsolute value of a measurement value having a generality can beoutputted, and using this output, a characteristic value can bemonitored at high sensitivity and accuracy, and a detailed determinationbecomes possible by applying a general data processing method utilizedin various fields at the present time such as a determination due towave analysis or time integral of variation.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of installation of ahigh-sensitivity measuring instrument according to an embodiment of thepresent invention.

FIG. 2 is a schematic diagram showing another example of installation ofa high-sensitivity measuring instrument according to an embodiment ofthe present invention.

FIG. 3 is a circuit diagram showing an example of constitution of amulti-dimension electric conductivity measuring instrument provided in asignal processor of the instrument depicted in FIGS. 1 and 2.

FIG. 4 is a circuit diagram showing another example of constitution of amulti-dimension electric conductivity measuring instrument provided in asignal processor of the instrument depicted in FIGS. 1 and 2.

FIG. 5 is a chart showing a result of a test carried out for confirmingthe performance of a high-sensitivity measuring instrument according tothe present invention.

FIG. 6 is a chart showing a result of another test carried out forconfirming the performance of a high-sensitivity measuring instrumentaccording to the present invention.

THE BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will beexplained referring to the drawings.

In the present invention, the characteristic of a substance beingmeasured, which is a target for measurement, is not limited to electricconductivity, and the present invention can be applied to measurement ofsubstantially any characteristic, but the following explanation will bedescribed mainly with respect to a case of measurement of electricconductivity.

FIGS. 1 and 2 exemplify cases where a high-sensitivity measuringinstrument according to the present invention is applied to an electricconductivity measurement system for a fluid, for example, water flowingin a pipe as a substance being measured 4. In a high-sensitivitymeasuring instrument 1 shown in FIG. 1, sensor A (2) and sensor B (3)for detecting electric conductivity are provided respectively at theupstream side and the downstream side of the substance being measured 4.The substance being measured 4 through sensor A and also passes throughsensor B, that is, the substance being measured 4 comes into contactwith sensors A and B with a specified time difference, and it ispossible that detection signals from both sensors are taken outsimultaneously. In a signal processor 5 provided are a multi-dimensionelectric conductivity measuring instrument capable of outputting adifference between detection signals taken out from both sensorssimultaneously at a certain time (exemplified in FIGS. 3 and 4), and acalculation processing part wherein using the difference as a differencebetween characteristic values at that time and at a time before or afterthe above-described time difference (namely, as a difference betweencharacteristic values upon elapsing the specified time difference), areference time of measurement and a reference characteristic at thattime are preset, a time axis having a time pitch of the specified timedifference is set, and a measurement value can be obtained at a point intime elapsing an arbitrary time pitch from the reference time.

In a high-sensitivity measuring instrument 11 shown in FIG. 2, a samplewater sampled from an identical position as an object for measuringelectric conductivity comes into contact with sensor A (2) as it is, andcomes into contact with sensor B (3) via a time delay column 12 capableof being adjusted in time, and a specified time difference is giventhrough the time delay column 12. Other structure is substantially thesame as that of the embodiment shown in FIG. 1.

First, examples of constitution of a multi-dimension electricconductivity measuring instrument provided in signal processor 5 will beexplained referring to FIGS. 3 and 4. In a multi-dimension electricconductivity measuring instrument 21 shown in FIG. 3, at least twosensors A and B (2, 3) for measurement of electric conductivity eachhaving at least two electrodes (in this embodiment, shown as athree-electrode structure) touching a substance being measured areprovided. In this embodiment, respective sensors A and B (2, 3) areelectrically connected so that the detection signals themselves from therespective sensors are processed by addition.

Respective sensors A and B (2, 3) are connected electrically in parallelto each other, an AC current is supplied from an AC oscillator 24provided as a power source to electrodes 22 a, 23 a of the respectivesensors for current supply at a condition of the same phase. Electrodes22 b, 23 b of respective sensors A and B (2, 3) for electricconductivity detection are electrically connected to each other, and thevalues of the detection signals themselves from both detectionelectrodes 22 b and 23 b are added to each other. Further, in thisembodiment, a multiplier or divider 25 for multiplying the value of thesupplied current at a predetermined magnification or for dividing it ata predetermined rate is provided at a position before electrode 22 a forcurrent supply to one sensor A (2), and it is possible to differentiatethe level of the electric conductivity of a substance being measured tobe detected by sensor A (2) as compared with that of sensor B (3).Namely, an AC current before being supplied to electrode 22 a forcurrent supply is amplified or attenuated at a predeterminedmagnification. In such a structure, it becomes possible to detect avariation in time of electric conductivity of a substance beingmeasured, which comes into contact with the respective sensors with aspecified time difference, at an optimum sensitivity.

The above-described processed signals, that is, the signals obtainedfrom electrodes 22 b and 23 b for electric conductivity detection areamplified as an output signal having an adequate level by a singleamplifier 26. At that time, an optimum range depending upon an objectivemeasurement can be selected by a measurement range switching device 27.

In this embodiment, the signal from amplifier 26, after a temperaturecompensation for measurement environment is carried out by a temperaturecompensator 28, is synchronized with the output side of AC oscillator24, and further, is amplified by an amplifier 31 with a range adjustor30 so that the signal becomes a signal having a level optimum forcontrol or output display to be employed, and the signal is taken out asan actual output 32.

In a multi-dimension electric conductivity measuring instrument 41 shownin FIG. 4, as compared with the embodiment shown in FIG. 3, a multiplieror divider 42 for multiplying the value of the supplied current at apredetermined magnification or for dividing it at a predetermined rateis provided at a position before electrode 23 a for current supply ofsensor B (3), and it is possible to differentiate the level of theelectric conductivity of a substance being measured to be detected bysensor B (3) as compared with that of sensor A (2). Namely, an ACcurrent before being supplied to electrode 23 a for current supply isamplified or attenuated at a predetermined magnification. The multiplieror divider has also a function to reverse the phase of the supplied ACcurrent. In such a structure, the detection signals themselves fromrespective sensors A, B (2, 3) are substantially processed bysubtraction, and the signal after the subtraction processing is sent toamplifier 26. The structure of other parts is substantially the same asthat of the embodiment shown in FIG. 3.

In the above-described multi-dimension electric conductivity measuringinstruments 21 and 41, since the detection signals from sensors A, B (2,3) are taken out simultaneously at a certain time, and a differencebetween the simultaneously taken-out signals is outputted, it becomespossible to remove an influence ascribed to outside disturbance ornoise, and only the above-described difference is outputted at a highaccuracy and a high sensitivity. In the present invention, using thisoutput of the difference, the following processing is carried out in thecalculation processing part provided in signal processor 5. Namely, theabove-described difference is used as a difference betweencharacteristic values upon elapsing a specified time difference, areference time of measurement and a reference characteristic value atthat time are preset, a time axis having a time pitch of the specifiedtime difference is set, and a measurement value is obtained at a pointin time elapsing an arbitrary time pitch from the reference time.

The basic concept of this calculation processing will be explained.

In the above, because a signal difference (D_(A−B)(t)) between a signalof sensor A (F_(A)(t)) and a signal of sensor B (F_(B)(t)) at a certaintime is obtained and the signal of sensor B (F_(B)(t)) indicates anabsolute value of a characteristic (electric conductivity in theabove-described embodiment) at a point before elapsing the specifiedtime difference, the following equation stands.F _(A)(t)=D _(A−B)(t)+F _(B)(t)  (1)

In practice, there is a case where F_(A)(t), F_(B)(t) and D_(A−B)(t) arenot in a same data line, and therefore it is necessary to mutuallyconvert the data depending on the utilization method when calculatingthese data, but this does not affect the essence of the presentinvention. Therefore, the indication is simplified in order tofacilitate the explanation.

The inventors of the present invention paid attention to the fact thatthe signal difference D_(A−B)(t) corresponds to the time differencebetween sensor A and sensor B, and considered that by utilizing thiscorrespondence, a sensor sole signal, that is, a signal corresponding toan absolute value of characteristic can be derived. In the presentinvention, the above-described difference (that is, D_(A−B)(t)) istreated as a variation in time of a signal as if the signal weredetected by a single sensor between at that time and at a time before orafter that time by the aforementioned time difference. Namely, when aspecified time difference between sensors A and B is referred to as DT,D_(A−B)(t) is used as a difference of characteristic value at a pointupon expiring DT. A time axis is set by setting this DT as a time pitch,and relatively to the reference characteristic value preset at thereference time, a measurement value at a point in time elapsing anarbitrary time pitch from the reference time is calculated as follows.

The relationship between F_(A) and F_(B) is represented as follows byusing the specified time difference DT between sensors A and B.F _(B)(t)=F _(A)(t−DT)  (2)From the equations (1) and (2), the following equation is led.F _(A)(t)=D _(A−B)(t)+F _(A)(t−DT)  (3)Namely, the signal (F_(A)(t)) of sensor A at an arbitrary time t becomesa signal calculated by adding a signal difference between sensors A andB (D_(A−B)(t)) to a signal of sensor A at a point before the time ofDT(F_(A)(t−DT)). By this, it becomes possible to treat the valueobtained by the equation (3) as an absolute value signal detected by asingle hypothetical sensor.

Further, because the equation:F _(A)(t−DT)=D _(A−B)(t−DT)+F _(A)(t−2DT)is derived, the following equation stands.F _(A)(t)=D _(A−B)(t)+D _(A−B)(t−DT)+F _(A)(t−2DT)

Further, because the equation:F _(A)(t−2DT)=D _(A−B)(t−2DT)+F _(A)(t−3DT)is derived, the following equation stands.F _(A)(t)=D _(A−B)(t)+D _(A−B)(t−DT)+D _(A−B)(t−2DT)+F _(A)(t−3DT)

By repeating similar operations, the following equation stands.F _(A)(t)=(D _(A−B)(t)+D _(A−B)(t−DT)+D _(A−B)(t−2DT)+ . . . +D_(A−B)(t−nDT))+F _(A)(t−(n+1)DT)

Where, although (D_(A−B)(t)+D_(A−B)(t−DT)+D_(A−B)(t−2DT)+ . . .+D_(A−B)(t−nDT)) is obtained by adding up the signal differences ofD_(A−B)(t−iDT) provided as a general equation (i=0−n, “n” is a number ofDT up to reach a previous certain reference time) by a time pitch of DT,even if traced back to any point, finally F_(A)(t−(n+1)DT) is left.Therefore, in the present invention, it is supposed to input a certainknown value into F_(A)(t−(n+1)DT). Namely, by inputting a value at aninitial step of the above-described calculation as a referencecharacteristic value, it becomes possible to calculate a signal of onlythe sensor as a relative value relative to this reference characteristicvalue. If a reference value is an absolute value of a characteristic, avalue added with the above-described variation can also be obtained asan absolute value of the characteristic to be measured as an object, anda variation of absolute value itself can be outputted. Although anyvalue may be used as this reference characteristic value as long as thevalue is a known value, usually, it is understandable to employ a value,at a state where a signal difference between sensors A and B is zero ata condition that a particular signal does not enter, as the referencevalue. Further, as aforementioned, it is also possible to set a valuewhose absolute value is not known as a comparative reference value forcalculating a measurement value, that is, the above-described referencecharacteristic value.

In the above-described calculation, it is also possible to calculate asignal of a sole sensor at a certain time, or to output sensor signalsin order accompanying with time expiration, by analyzing after datacollection. The steps are as follows for example.

(1) Setting of Parameter:

In a case of digital processing, although a time pitch within a DT timetheoretically can be set arbitrarily, usually it is easy to set a timepitch at an equal interval. Further, if an appropriate analog circuitcan be assembled, it may be employed. Hereinafter, a digital processingcase will be explained wherein a time pitch within a DT time is set atan equal interval.

The time pitch within a DT time is referred to as “δt” and an arbitrarytime “t” on a time axis is indicated as t=mDT+nδt. Where, “m” and “n”are integers, and “n” is 0–N, N=DT/δt.

By this, at an arbitrary time “t”, the signal of sensor A isF_(A)(mDT+nδt), the signal of sensor A is F_(B)(mDT+nδt), and a signaldifference is D_(A−B)(mDT+nδt).

A signal of a sole sensor to be determined is referred to as X(mDT+nδt).

Where, a parameter capable of being observed is D_(A−B)(mDT+nδt), forexample, due to the aforementioned multi-dimension electric conductivitymeasuring instrument.

(2) Input of Initial Value

A initially set known value is inputted at least as DT time, and a knownvalue is set as a reference characteristic value at a reference time indata series of a sole sensor signal.

Here, the initial known reference characteristic value is set to bezero. Therefore, at m=0, X(nδt)=0 at n=0–N.

(3) Measurement

-   When a value before DT time is used, the following equation stands.    X(mDT+nδt)=X((m−1)DT+nδt)+(D _(A−B)(mDT+nδt)  (4)-   When determined from the initial value, the following equation    stands.    X(mDT+nδt)=X(nδt)+(integral of i=1–m of D _(A−B)(iDT+nδt))  (5)

Thus, data in time sequence at respective points in time elapsingrespective time pitches from the reference time can be obtained as dataof measurement values, and the data in time sequence can comprise aplurality of groups of data in time sequence which are obtained bydividing with a pitch of δt smaller than the specified time differenceDT.

(4) Storing of Data

In the above-described procedure, in a case of equation (4), it can beprocessed by storing N data of X(mDT+nδt) within a immediately previoustime DT. In a case of equation (5), although it is necessary to storeall previous data of X(mDT+nδt), in this case, it is possible toindicate all past data.

By carrying out the above-described calculation, for example, themeasurement in a measurement system as shown in FIG. 1 has been carriedout. The result of the measurement is shown in FIGS. 5 and 6. FIG. 5shows an example of measurement in a case where a temporary variation ofelectric conductivity occurred, and FIG. 6 shows an example ofmeasurement in a case where a variation of electric conductivity with acertain continuous time occurred. In FIGS. 5 and 6, “a difference inconductivity” indicates only a variation of electric conductivityoutputted from a difference signal of sensors A and B, and “an absoluteconductivity -1-” is an electric conductivity detected by a sensorprovided at a downstream position separately from sensors A and B and isoutputted for confirming the effectiveness of the present invention. “Anabsolute conductivity -2- (calculated from difference in conductivity)”indicates an absolute value of electric conductivity as an objectivehigh-sensitivity measurement value which is calculated by adding thedifference in conductivity to the above-described preset referencecharacteristic value.

In both FIGS. 5 and 6, the absolute conductivity -2- extremely preciselyindicates substantially the same characteristic as the characteristicmeasured as the absolute conductivity -1-, and it is understood that themeasurement by the high-sensitivity measuring instrument according tothe present invention has been carried out at a high sensitivity.Further, in the high-sensitivity measuring instrument according to thepresent invention, because it is possible that a difference betweendetection signals of sensors A and B outputted as a high-accuracyobservation value is outputted as an absolute value added to a knownreference value, the accuracy of the absolute value as the outputtedmeasurement value can also be maintained surely at a high level. Namely,a high-sensitivity and high-accuracy measurement becomes possible.

Although the above-described explanation has been carried out mainly asto the measurement of electric conductivity, the high-sensitivitymeasuring instrument according to the present invention can be appliednot only to this, but also to basically any measurement system requiringthe determination of a variation of an absolute value of an objectivecharacteristic to be measured or a relative variation from a certainreference value as the case may be. Therefore, the present invention canbe applied to any measuring instrument requiring a high-sensitivitymeasurement at an excellent S/N ratio, for example, a measurement ofultraviolet ray, a measurement of differential refractive index, ameasurement of fluorescent luminous intensity, an electrochemicalmeasurement, a measurement of fine particles, etc.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The high-sensitivity measuring instrument according to the presentinvention can be applied to any measurement system requiring adetermination of a variation of an absolute value of an objectivecharacteristic to be measured or a relative variation from a certainreference value. The high-sensitivity measuring instrument according tothe present invention exhibits remarkable advantages when it is usedparticularly as a detector in ion chromatography or liquidchromatography requiring a high-sensitivity measurement ofcharacteristics in a fluid at a high S/N ratio, or as a monitor forobserving a minute concentration of impurities contained in a ultra purewater.

1. A high-sensitivity measuring instrument comprising: a) at least twosensors adapted to detect the same characteristic of a substance broughtinto contact with said sensors; and b) a signal processor operablylinked to both of said at least two sensors; wherein said at least twosensors are positioned so that they contact the substance at differenttimes characterized by a specified time difference; and wherein thesignal processor calculates a difference between detection signals takenout simultaneously from said at least two sensors, calculates adifference between characteristic values upon elapsing said specifiedtime difference, presets a reference characteristic value at thatreference time, sets a time axis having a time pitch of said specifiedtime difference, and calculates a measurement value at a point in timeelapsing an arbitrary time pitch from said reference time.
 2. Thehigh-sensitivity measuring instrument according to claim 1, wherein datain time sequence at respective points in time elapsing respective timepitches from said reference time are obtained as data of measurementvalues.
 3. The high-sensitivity measuring instrument according to claim2, wherein said data in time sequence comprise a plurality of groups ofdata in time sequence including data in time sequence, a position of atime pitch of which is present within said specified time difference. 4.The high-sensitivity measuring instrument according to claim 1, whereina substance being measured for reference is brought into contact withsaid sensors, and an output value thereof in said measuring instrumentis set as said reference characteristic value.
 5. The high-sensitivitymeasuring instrument according to claim 1, wherein a substance beingmeasured for reference having a known characteristic value is broughtinto contact with said sensors, and said reference characteristic valueis set so that an output value thereof in said measuring instrumentbecomes said known characteristic value.
 6. The high-sensitivitymeasuring instrument according to claim 1, wherein said substance beingmeasured is a fluid.
 7. A method for measuring a characteristic value ofa substance at a given point in time, said method comprising: a)providing the high-sensitivity measuring device according to claim 1; b)bringing the at least two sensors into contact with said substance; andc) processing detection signals from said at least two sensors in saidsignal processor to give a measurement of the characteristic value ofthe substance at a given point in time.